Liquid crystal display devices are characterized by the high quality of images, the small thickness, the light weight and the small consumption of electric power and widely used for televisions, personal computers and automobile navigators. It has been pointed out that liquid crystal display devices have a drawback in that brightness, color and contrast vary to a great extent and difficulty arises in watching images when the images are observed at oblique angles.
To overcome the drawback, improvements in the design of the liquid crystal cell itself have been studied, and a liquid crystal display device of the in-plane switching mode is proposed as one of the improvements (for example, Patent Reference 1). In accordance with the proposed technology, the angle of field is improved in comparison with that of liquid crystal display devices of other modes. However, in accordance with this technology, the arrangement of polarizer plates shifts from the cross-nichol arrangement depending on the angle of observation, and this causes a decrease in the angle of field due to leak of light although the decrease in the angle of field due to the liquid crystal molecules in the liquid crystal cell is relatively suppressed. Moreover, further improvement is desired with respect to the narrow angle of field due to the liquid crystal molecules in the liquid crystal cell. Therefore, it is attempted that the decrease in the contrast of images is suppressed by adding a means for optical compensation to the liquid crystal display devices of the in-plane switching mode.
For example, a liquid crystal display device in which a sheet for optical compensation is disposed between a liquid crystal cell and at least one of polarizer plates, the sheet for optical compensation is optically negatively uniaxial, and the optical axis is parallel to the face of the sheet, is proposed (Patent Reference 2).
As another liquid crystal display device of the in-plane switching mode, a liquid crystal display device in which a first polarizer plate, a film for optical compensation, a first substrate, a liquid crystal layer, a second substrate and a second polarizer plate are disposed in this order, one of the polarizer plates has a transmission axis parallel to the slow axis of the liquid crystal during the dark display of the liquid crystal layer, and the angle between the slow axis of the film in the sheet for optical compensation and the transmission axis in one of the polarizer plates is 0 to 2° or 88 to 90°, is proposed (Patent Reference 3).
However, none of these means are sufficient for providing a liquid crystal display device which exhibits uniform display of images with a great contrast at any angle of observation, and further improvement has been desired.
[Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei 7(1995)-261152
[Patent Reference 2] Japanese Patent Application Laid-Open No. Heisei 10(1998)-054982
[Patent Reference 3] Japanese Patent Application Laid-Open No. Heisei 11(1999)-305217